Magnetic disk apparatus

ABSTRACT

A magnetic disk apparatus arranged in a housing having a plurality of magnetic disks stacked on a rotating shaft, arms supporting thereon magnetic heads and adapted to be inserted between said magnetic disks, a rotary actuator for moving the arms, a housing forming at least a part of an arcuate-shaped shroud which substantially surrounds a portion of side surfaces of the magnetic disks so as to permit movement of the arms and which is concentric with the magnetic disks so as to define a gap between the shroud and the portion of the side surfaces of said magnetic disks. The gap defined between the outer peripheral end surfaces of the magnetic disks and the shroud is in a range of 0.1 mm to 0.6 mm.

REFERENCE TO RELATED APPLICATION

This is a continuation-in-part application of U.S. application Ser. No.09/356,056, filed Jul. 16, 1999, now U.S. Pat. No. 6,369,978, thesubject matter of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

The invention relates to a magnetic disk apparatus, and moreparticularly, a housing structure of a magnetic disk apparatus, whichhouses therein a plurality of stacked rotating disks for reading andwriting information and a rotary actuator supporting a head for readingand writing information on the disks, such that the head is movablebetween the disks.

With conventional magnetic disk apparatuses, turbulence of an airflowing between disks causes vibration of the disks called “flutter”.When a head is positioned on a disk generating such flutter, the head isdegraded in positional accuracy with respect to tracks for reading andwriting of information.

As a prior art (1), Japanese Patent Unexamined Publication No. 10-162548describes a method for forcedly generating an airflow directed to outerperipheries of disks from inner peripheries thereof. As a further priorart (2), there has been proposed a method for reducing a spacing betweenrotating disks and a housing called a “shroud” which surrounds the disksand is formed concentrically with the disks. Such a shroud is a part ofthe housing that is disposed in a magnetic disk apparatus to covercomponents such as magnetic disks, an actuator for positioning of ahead, and the like, the shroud surrounding side surfaces of the disks.

An airflow generated around rotating disks includes a primary flow, inwhich air is dragged by revolution of the disks to flow in acircumferential direction, and a secondary flow, in which air in thevicinity of disk surfaces flows toward outer peripheries of the disksand air between the disks flows toward inner peripheries of the disks.Since the secondary flow involves unstable air turbulence, the prior art(1) is directed to suppressing the occurrence of flutter by generating aforced airflow directed toward the outer peripheries of the disks fromthe inner peripheries thereof so as to reduce the unstable airflowcaused by the secondary flow.

The prior art (2) is directed to reducing flutter by decreasing a gapbetween disks and a shroud to suppress that incoming and outgoing of airon the top and bottom surfaces of disks, which would be produced in theevent of the gap between the disks and the shroud being large, toprevent a pressure difference between the top and bottom surfaces fromvarying with the passage of time.

As a prior art (3), Japanese Patent Unexamined Publication No. 7-320478describes a housing structure making use of an airflow circulating in ahousing of a magnetic disk apparatus for other purposes than reductionof flutter, and discloses a method for removing dust by means of afilter and cooling an interior of the housing.

If the housing structure of a magnetic disk apparatus is the same,flutter caused by turbulence of an air flowing between disks increasessubstantially in proportion to a square of a disk radius and the numberof revolutions of the disks. Therefore, a housing structure is needed,which reduces flutter having an adverse influence on head positionalaccuracy, in reduction of track intervals making magnetic disks high incapacity and in increase in the number of revolutions required forachieving high speed.

Provided that the housing structure of a magnetic disk apparatus is thesame, the driving power for revolution of disks is substantiallyproportional to third power of the number of revolutions and fifth powerof a disk radius. Accordingly, as with flutter mentioned above, it isnecessary to obtain a housing structure that reduces an airflow tendingto impose a burden on a rotating driving force, thus reducing a diskdriving power in increasing the number of revolutions required formaking the magnetic disk apparatus high in speed.

However, the method for forcedly generating an airflow directed towardouter peripheries of disks from inner peripheries thereof offers thefollowing problem. Such method for forcedly generating an airflowdirected toward outer peripheries of disks from inner peripheriesthereof becomes ineffective because respective arms of a rotary actuatoradapted to be inserted between stacked disks block the airflow directedtoward the outer peripheries of the disks from the inner peripheriesthereof if these arms have a thickness of half or more of an intervalbetween the disks.

Also, the method, in which a gap between disks and a housing called a“shroud” and formed concentric with rotating disks is made small, offersthe problem set forth below.

With the method, in which a gap between disks and a housing called a“shroud” and formed concentric with rotating disks is made small, one ofthe causes for occurrence of flutter can be dissolved because it ispossible to suppress fluctuation of pressure difference with the passageof time, which is caused by incoming and outgoing of an airflow on topand bottom surfaces of the disks, even when arms of the rotary actuatorare inserted between the disks. However, when the arms are insertedbetween the disks, they will block the primary airflow, which is draggedby the revolving disks to flow in the circumferential direction. As aresult, a high pressure region is generated on an upstream side of thearms while a low pressure region is generated on a downstream side ofthe arms.

In addition, an air flowing in the circumferential direction on theupstream side of the arms is curved toward the inner peripheries of thedisks by the arms to produce a high speed flow directed toward the innerperipheries of the disks. Since such flow directed toward the innerperipheries of the disks tends to return around tip ends of the arms tothe outer peripheries of the disks, so it will merge with a flow on thedownstream side of the arms to generate turbulence, so that pressuredifference between the high pressure on the upstream side of the armsand the low pressure on a downstream side of the arms fluctuates. Suchpressure fluctuation causes not only flutter but also a fluctuatingforce called “wind turbulence” tending to swing the arms. Such swingingof the arms is also responsible for degradation of the head positionalaccuracy in the magnetic disk apparatus.

Thus, either of the method for forcedly generating an airflow directedtoward outer peripheries of disks from inner peripheries thereof, andthe method, in which a gap between disks and a shroud is made small,disclosed in the prior art offers a problem that pressure fluctuationgenerated upon insertion of the arms between the disks cannot bereduced.

Meanwhile, the prior art (3) making use of an airflow circulating in ahousing of a magnetic disk apparatus also offers a problem set forthbelow.

The low pressure region produced on the downstream side of the armsdraws in air from outside of the disks. Therefore, when the shroudcovers the downstream side of the arms to decrease a gap between thedownstream side of the arms and the shroud, high speed airflow entersthrough the gap into spaces between the disks, thereby causing asignificant pressure fluctuation. Presence of a flow passage connectingthe upstream and downstream sides of the arms will reduce pressuredifference between the upstream and downstream sides of the arms. Thus,pressure loss caused by the insertion of the arms between the disks isreduced, so that the driving power for revolution of the disks iscorrespondingly reduced.

However, when a flow passage connecting the upstream and downstreamsides of the arms is defined in a rotating shaft of the rotary actuatoror inside the voice coil motor for driving of the actuator, itinevitably results in a narrow flow passage with many curves, and socauses a considerable pressure fluctuation between disks for the similarreason as mentioned above. The foregoing flow passage is effective inremoving dust and cooling the voice coil motor that generates heat.However, it is very likely that wind turbulence and flutter increasewhen airflow flows through the arm section and an interior of the voicecoil motor, which are complex in structure tending to easily developflow turbulence. In addition, it is unnecessary in a relativelysmall-sized magnetic disk apparatus to cool the voice coil motor.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a magnetic diskapparatus having a housing structure, which enables suppressing pressurefluctuation, which would occur when arms of a rotary actuator areinserted between the disks, to reduce flutter and wind turbulence.

Another object of the invention is to provide a magnetic disk apparatushaving a housing structure, which can prevent generation of additionalpressure fluctuation on upstream and downstream sides of arms, thusreducing driving power.

To these ends, the invention provides a magnetic disk apparatuscomprising a plurality of magnetic disks stacked on a rotating shaft,arms supporting thereon magnetic heads and adapted to be insertedbetween the magnetic disks, a rotary actuator for moving the arms, ahousing having an arcuate-shaped shroud, which surrounds the sidesurfaces of the magnetic disks so as to permit movements of the arms andwhich is concentric with the magnetic disks, a space opened from theshroud and located on a downstream side of the arms relative to an airflow, which is generated by the revolution of the magnetic disks andmoves on surfaces of the magnetic disks, an opening provided on theshroud on an upstream side of the arms relative to the airflow andhaving a greater width than that of a gap defined between the magneticdisks and the shroud, and a cover, which constitutes a part of theshroud to cover a voice coil motor for driving the rotary actuator, andforms between the cover and an inner wall of the housing a bypasschannel for providing communication between the opening and the openedspace, and wherein the bypass channel has a linear section of apredetermined length extending from the opening.

The housing structure comprises a space not covered by the shroud andprovided on a downstream side of the arms, and a channel, which connectsan upstream side of the arms to the space not covered by the shroud andprovided on the downstream side of the arms, the channel being providedwith a linear section, which has a rectifying effect on an airflow andhas a depth of five times or more a width of the channel and a length offive times or more the width of the channel.

According to a feature of the present invention, the bypass channel maybe constructed to have a depth of 5D or more in a direction parallel toa rotating shaft where D is a spacing or width of the linear section.

According to another feature of the present invention, the bypasschannel may be constructed to have a linear section having a length ofat least 5D or more where D is a spacing or width of the linear section.

In accordance with a further feature of the present invention, thebypass channel may be constructed to have a linear section having adepth of 5D or more and a length of at least 5D or more in a directionparallel to a rotating shaft where D is a spacing or width of the linearsection. In accordance with another feature, the cover may be configuredto cover at least a side surface of the voice coil motor.

According to a still further feature of the present invention, the covermay be a component which encloses a coil section of the voice coil motorand at least a side surface of which is closed to prevent airflow fromcoming into the voice coil motor from the bypass channel.

Still further advantages of the invention will become apparent to thoseof ordinary skill in the art upon reading and understanding thefollowing detailed description of the preferred and alternateembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in conjunction with certain drawingswhich are for the purpose of illustrating the preferred and alternateembodiments of the invention only, and not for the purposes of limitingthe same, and wherein:

FIG. 1 is a cross-sectional view illustrating a configuration of amagnetic disk apparatus in accordance with the invention;

FIG. 2 is a longitudinal sectional view illustrating a housing structureof the magnetic disk apparatus of the invention;

FIG. 3A through FIG. 3D are diagrams showing results of comparison inpressure fluctuation and power consumption of the device with andwithout a bypass channel in accordance with the invention;

FIG. 4 is a cross-sectional view illustrating a configuration of amagnetic disk apparatus according to a further embodiment of theinvention;

FIG. 5 is a cross-sectional view illustrating a configuration of amagnetic disk apparatus according to a still further embodiment of theinvention; and

FIG. 6 is a graph showing an inflow angle of an airflow relative to aratio of a length of the linear section and a channel width of thebypass channel.

DETAILED DESCRIPTION OF THE PREFERRED AND ALTERNATE EMBODIMENTS

An embodiment of the invention will be described with reference to FIG.1 through FIG. 3D. FIG. 1 is a cross-sectional view showing aconfiguration of a magnetic disk apparatus in accordance with theinvention.

FIG. 2 is a longitudinal sectional view illustrating a housing structureof the magnetic disk apparatus of the invention. FIGS. 3A through 3Dshow results of comparison in pressure fluctuation and power consumptionof the device with and without a bypass channel in accordance with theinvention.

As shown in FIG. 1, the magnetic disk apparatus according to theinvention is constructed as set forth below. A magnetic disk stack iscomposed of a plurality of disks 1 that are stacked on and fixed to amagnetic disk rotating shaft 2 connected to a spindle motor (not shown).Arms 4 are driven on a turning arm shaft 3. A coil (not shown) isprovided on the arms 4 toward the turning arm shaft 3 to drive the arms4, the coil and a magnet (referred to as a “voice coil motor 6” for thesake of convenience) provided on a side of a housing 10 constituting arotary actuator. Magnetic disk read/write head 5 are provided on tipends of the arms 4. A motor cover 21 is a part of the housing thatsurrounds the voice coil motor 6, which constitutes the rotary actuator.

In addition to the components mentioned above, an input/output signalwire 7 and a signal wire terminal 8 for the magnetic head 5, a filter 9for cleaning air in spaces between the magnetic disks, etc. are receivedin the housing 10 of the magnetic disk apparatus as required, andhermetically sealed to be isolated from the outside of the housing. Inthis embodiment, the filter 9 is provided, and an air inlet for thefilter 9 and an exhaust port are provided in a part of a shroud, whichcovers an outer periphery of the disks 1. However, it goes withoutsaying that the filter 9 may be omitted.

Referring to FIG. 1, a direction of revolution of the disks being fixedas indicated by an arrow 13, air flows between disks in the directionindicated by the arrow 13. With respect to the direction of the arrow13, an upstream side of the arms 4 is defined as a left side of the arms4 as viewed in the drawing, and a downstream side of the arms 4 isdefined as a right side of the arms 4 in the drawing. Ensured in an armdownstream space 11 located downstream of the arms 4 and outside theouter periphery of the disk stack 1 is a space, which is not occupied bythe shroud to be free from the shroud, and which allows all the arms 4of the rotary actuator to move about the shaft 3 outside the disk stack1.

As shown in FIG. 1, the signal wire 7 and the signal wire terminal 8 forinput/output for the magnetic head 5 are disposed in the above-mentionedspace. A shroud 12 a defines a part of the housing 10, which is formedto be concentric with the disk stack 1. A shroud 12 b constitutes a partof the housing structure of the magnetic disk apparatus, and alsodefines a part of the motor cover 21 in the embodiment of the invention.Like the shroud 12 a, the shroud 12 b is also shaped to be concentricwith the disk stack 1. Here, the concentric configuration means a shapehaving a wall surface that is equidistant from the rotating shaft 2, towhich the disk stack 1 is fixed.

In the embodiment of the invention, the shrouds 12 a and 12 b are formedto be concentric with the disk stack 1 in areas other than areas wherethe arm downstream space 11 and the air introduction passage into thefilter 9 are located. The motor cover 21 is disposed on the upstreamside of the shroud 12 b positioned on the upstream side of the arms suchthat a gap is provided between the motor cover and the inner wall of themagnetic disk apparatus housing 10 to form a shroud opening 12 c.

A bypass channel 15 is defined by forming side surfaces of the motorcover 21 and of the housing 10 to provide a parallel gap between theshroud opening 12 c and the arm downstream space 11. The shroud 12 b ofthe motor cover 21 located on the upstream side of the arms is providedin the vicinity of the arms 4 so as to block airflow toward the voicecoil motor 6 but not to interfere with the required turning of the arms4. In addition, the motor cover 21 may be formed either integrally withthe housing 10 or formed as a separate piece for assembly.

Air in the housing of the embodiment flows as indicated by an arrow 14in FIG. 1. Revolution of the disk stack 1 causes the air to flow in thecircumferential direction indicated by the arrow 13 between adjacentdisks, so that the air flow is blocked by the arms 4 to produce a highpressure area on the upstream side of the arms 4. On the other hand, theair pressure decreases on the downstream side of the arms 4 to cause anair in the arm downstream space 11 to be drawn into between the disks.Here, the bypass channel 15 connects the high pressure upstream side ofand the low pressure downstream side of the of the arms 4, so that theair flow is caused as indicated by an arrow 14.

The configuration of the bypass channel 15 will now be described withreference to FIG. 2 and FIG. 6. FIG. 2 is a longitudinal sectional viewshowing the housing structure of the magnetic disk apparatus inaccordance with the invention, in which a section associated with therotary actuator is omitted. FIG. 6 shows a relationship between aninflow angle of airflow and a ratio of a length of a linear section anda width of the bypass channel.

As shown in FIG. 2, the bypass channel 15 is composed of parallel wallsto have a larger width D (denoted by 17 in the drawing) than a gap h(denoted by 19 in the drawing) between the shroud 12 and the disk stack1 and a depth H (denoted by 18 in the drawing) equal to or more than theheight of the disk stack 1. The depth H should be five times or more thewidth D. Because of the depth H five times or more the width D, thepressure loss at the shroud opening 12 c can be maintained substantiallyat a constant level even when the direction of the airflow entering intothe bypass channel 15 from the shroud opening 12 c as shown in FIG. 1varies depending on the position of the arms 4. Therefore, the provisionof the bypass channel 15 can be effective reducing pressure fluctuationirrespective of the position of the arms 4.

Moreover, the bypass channel 15 is provided with the linear section,which has a length L (denoted by 16 in the drawing), as shown in FIG. 1,corresponding to five times or more the width D. The flow entering intothe bypass channel 15 sometimes comes off to generate a pulsating flowat a tip end, which forms a part of the motor cover 21 toward the shroudopening 12 c and at which the bypass channel 15 is in contact with theshroud 12 b. Even when such pulsating flow is generated, the linearsection having the length L can attenuate flow speed fluctuation becausethe length L is at least five times the width D. Since coming-offtending to generate an airflow turbulence takes place mostly at theshroud opening 12 c, it suffices that the linear section is located onthe downstream side of the shroud opening 12 c. So, portions of thebypass channel 15 except the linear section does not need to have awidth D of one fifth or less of the depth H and a rectangular-shapedcross section as shown in FIG. 2.

Relationships among the length of the bypass channel and so on will bedescribed with reference to FIG. 6.

The axis of abscissa in a graph shown in FIG. 6 indicates an inflowangle of an air flow entering into the bypass channel. With the magneticdisk apparatus, such inflow angle varies depending on a manner ofmounting the opening or a position of the arms of the rotary actuator. Atangent line of the disk stack 1 serves as a reference for the inflowangle. Herein, such reference is provided by a tangent line at an end ofthe disk stack 1 closest to the side face of the magnetic diskapparatus, in which the bypass channel 15 is formed. A line 601 in thegraph indicates an inflow angle, at which air can flow into the bypasschannel 15 despite of a pressure loss in the bypass channel 15. Thus,the bypass channel in accordance with the invention is made effective inan area 603 on the left side of the line 601 in the graph.

The axis of ordinate in FIG. 6 indicates a ratio of length to width L/Dof the linear section. A curve 602 plots values of L/D of a linearsection L required for airflow turbulence to assume a constant value inthe bypass channel, relative to respective inflow angles. The bypasschannel exhibits a rectifying effect in a region above the curve 602. Asshown in the graph, an intersection point of the line 601 and the curve602 is in most cases near a point where the value of L/D assumes 5. Itis seen that, with the value of L/D being 5 or more, airflow isgenerated in the bypass channel irrespective of the manner of mountingof the opening and the position of the arms of the rotary actuator, andthat turbulence is attenuated in the linear section to provide therectifying effect.

The analysis results shown in FIG. 6 are ones when the width D of thelinear section is one fifth or less of the depth H, and are almost thesame when the value of H/D is 5 or more. When the value of H/D issmaller than 5, the bypass channel is increased in pressure loss.Therefore, no airflow is sometimes generated in the bypass channeldepending on the position of the arms of the rotary actuator, so thatadvantages of the invention cannot be obtained.

Likewise, if the width D of the bypass channel is smaller than theshroud gap h, then the bypass channel is sometimes increased in pressureloss, and advantages of the invention cannot be obtained. Thus, asdescribed above, advantages of the invention can be obtainedirrespective of the manner of mounting of the opening and the positionof the arms of the rotary actuator, provided that the channel width D ofthe linear section of the bypass channel is greater than the shroud gaph, the length L of the linear section is 5D or more, and the depth H ofthe linear section is also 5D or more.

In this manner, a pressure difference between the high-pressure upstreamside of and the low-pressure downstream side of the arms 4 decreases.Furthermore, since airflow is rectified in the linear section of thebypass channel 15, an airflow free from turbulence comes into the armdownstream space 11 to be reduced there in speed, and slowly enters intospaces between adjacent disks so as not to impede airflow accompanyingthe revolution of the disk stack 1. As described above, the airflow inthe housing in accordance with the invention reduces the pressure loss,which would generate due to the pressure difference between the upstreamside of and the downstream side of the arms 4 as the result of thepresence of the arms to thereby reduce the driving torque required forrevolution of the disk stack 1 and to control an amplitude offluctuations in pressure difference between the upstream side of and thedownstream side of the arms 4 with the passage of time, which isresponsible for wind turbulence. Further, airflow entering into thespaces between adjacent disks at the downstream side of the arms isreduced in turbulence with the result that flutter is reduced.

With reference to FIG. 3, advantages of the invention will now bedescribed by way of results obtained by analysis of unsteady flow. FIG.3A shows results obtained when disks have a diameter of 65 mm, a gap hbetween the shroud and the disks is 0.7 mm, and the disks revolve at12000 rpm.

A configuration 1 is shown in FIG. 3B, a configuration 2 is shown inFIG. 3C, and a configuration 3 is shown in FIG. 3D. FIG. 3A showscomparison among these three configurations with respect to a degree ofinfluence (304) of flutter on positional accuracy, a degree of influence(305) of wind turbulence on the positional accuracy, and a ratio (306)of power consumption for revolutions every disk. All the configurationsshown in FIGS. 3B through 3D are the same except the shape of thehousings.

Configuration 1 is not equipped with the bypass channel 15 of theinvention, and the shroud 12 covers the upstream side of the arms 4. Inconfiguration 1, air flows through a gap between the arm rotating shaft3 and the voice coil motor 6 as indicated by an arrow 300 in FIG. 3B.

The configurations 2 and 3 are equipped with the bypass channel 15 ofthe invention that has a width D of 2 mm and a depth H of 20 mm. Withthe configuration 2, the motor cover 21 of the invention is formed of aflat plate, and the linear section L of the bypass channel isapproximately 10 mm. Furthermore, with the configuration 2, a gapbetween the rotating shaft 3 of and the voice coil motor 6 of the rotaryactuator is not closed. Accordingly, almost the air flows as indicatedby an arrow 301 in the drawing while a part of the air flows in thevoice coil motor as indicated by an arrow 302 in the drawing.

With the configuration 3, the gap is closed, so that the air flows asindicated by an arrow 303. Like the degree of influence (304) of flutteron the positional accuracy, the degree of influence (305) of windturbulence on the positional accuracy and the power consumption ratio(306) are indicated with those for the configuration 1 being 100%. Asapparent from FIGS. 3A through 3D, the bypass channel 15 of theinvention reduces the power consumption as well as the influences of theflutter and wind turbulence.

Another embodiment of the invention will be described with reference toFIG. 4. FIG. 4 is a cross-sectional view showing a configuration of amagnetic disk apparatus in another embodiment, to which the invention isapplied. This embodiment differs from the embodiment shown in FIG. 1 ina manner of forming a bypass channel 15.

In the embodiment, components such as a shroud 12 a and a filter 9 arethe same as those shown in FIG. 1. An arm downstream space 11 is notprovided with any shroud whereby a space sufficient to permit all arms 4of the rotary actuator to move about a shaft 3 outside a disk stack 1 isensured. As with the configuration shown in FIG. 1, a signal wire 7 anda signal wire terminal 8 for input/output of a magnetic head 5 arearranged in the space.

As shown in FIG. 4, a motor cover 21 in the embodiment is formed byhaving a shroud of a housing 10 extended to an upstream side of the arms4 and cutting off the same partly for the provision of an opening 12 c.A guide vane 20 for defining the bypass channel 15 is formed by mountinga plate, which has been made separately from the housing 10, so as tomake the same parallel to the inner wall of the housing 10.

In the embodiment shown in FIG. 4, the guide vane 20 is bent downstreamof the linear section of the bypass channel 15 so as to block airflowinto a voice coil motor 6. Further, a wall surface of the bypass channel15, which mates with the guide vane 20, may not be defined by the innerwall of the housing 10 but may be defined by mounting a flat plate tothe housing 10 like the guide vane 20. According to this embodiment, itis simply possible to obtain the same effect as that in the aforesaidembodiment shown in FIG. 1 without forming the housing 10 in complicatedmanner.

A further embodiment of the invention will be described with referenceto FIG. 5. FIG. 5 is a cross-sectional view showing a configuration of amagnetic disk apparatus in the further embodiment, to which theinvention is applied.

This embodiment differs from the embodiment shown in FIG. 1 in a mannerof forming a bypass channel 15 and a shroud 12 b on an upstream side ofthe arms. In the embodiment, components such as a shroud 12 a and afilter 9 are the same as those shown in FIG. 1. An arm downstream space11 is not provided with any shroud whereby a space sufficient to permitall arms 4 of the rotary actuator to move about a shaft 3 outside a diskstack 1 is ensured. As with the configuration shown in FIG. 1, a signalwire 7 and a signal wire terminal 8 for input/output of a magnetic head5 are arranged in the space.

Further in this embodiment, a spacing 30 between the outer peripheralend surfaces of the magnetic disks and the shroud 12 a is 0.1 to 0.6 mmand generally larger than 0.1 mm and smaller than 0.6 mm. Also, anopening 12 c is provided on an upstream side of the arms 4 of theactuator and an open space 11 is provided on a downstream of the arms 4of the actuator, the opening 12 c and the open space 11 beingcommunicated to each other by a bypass channel 15, which is defined by amotor cover 21 a and an inner side surface of the housing 10. Also, ashroud 12 b is formed between a voice coil motor and the magnetic disks1. The motor cover 21 a is desirably closed so as to prevent an air flowin the bypass channel 15 from entering the voice coil motor. However,only a portion in the vicinity of the opening 12 c may be of closedconstruction so that the construction of the motor cover 21 a befulfilled by the voice coil motor. This becomes less effective inreducing a change in flow velocity in the return channel but isexcellent in productivity because of no need of the provision of themotor cover 21 a.

In the embodiment, the narrow shroud can reduce flutter of the disks.Also, the provision of the bypass channel communicating between theopening 12 c and the open space 11 makes it possible to preventfluctuation in a difference between high pressure on the upstream sideof and the downstream side of the arm. Thereby, flutter can be reduced,and fluctuant forces called wind turbulence and tending to swing the armcan be suppressed. In this manner, narrowing of the shroud andemployment of the bypass channel makes it possible to reduce flutter andsuppress wind turbulence caused by the arm. Only when these twotechniques are used in combination, flutter and vibrations of the armcan be suppressed to realize a magnetic disk apparatus of high speedrotation.

In the embodiments shown in FIGS. 1 and 4, the motor cover 21 isprovided to constitute the bypass channel 15 and the shroud 12 b on theupstream side of the arms, while in this embodiment any motor cover 21is not provided and an inner wall of the housing 10 is made a shroudwhich extends from a shroud 12 a to an area, in which an opening 12 c isprovided, to be concentric with the disk stack 1 except inlet and outletof air into a filter 9. The remaining inner wall surface of the housingis formed to be flat.

Then, a side surface 12 b opposed to the disk stack is formed on acasing 22 of a voice coil motor 6 to be arcuate in concentric mannerwith the disk stack 1. Further, a side surface 21 a of the casing 22opposed to the housing 10 is formed to be flat in parallel to a planarportion of the inner side surface of the housing 10. Here, the sidesurface 12 b and the side surface 21 a are contiguous backward in FIG. 5to be closed at least for the purpose of blocking air flowing into thevoice coil motor from the bypass channel 15.

Without the provision of any motor cover 21, the bypass channel 15described in the embodiment of FIG. 1 can be constructed by fixing thevoice coil motor, which is provided with the casing 22 formed in thismanner, to the housing 11 of the magnetic disk apparatus. Thus,according to this embodiment, it is possible to obtain the same effectas that in the embodiment of FIG. 1 simply by changing the voice coilmotor and without forming the housing 10 in complicated manner.

The invention can realize a magnetic disk apparatus having a housingstructure, which enables suppressing pressure fluctuation, which wouldoccur when arms of a rotary actuator are inserted between the disks, toreduce flutter and wind turbulence and prevent generation of additionalpressure fluctuation upstream and downstream of the arms, thus reducingdriving power.

What is claimed is:
 1. A magnetic disk apparatus arranged in a housingcomprising a plurality of magnetic disks stacked on a rotating shaft,arms supporting thereon magnetic heads and adapted to be insertedbetween said magnetic disks, a rotary actuator for moving said arms, ahousing forming at least a part of an arcuate-shaped shroud whichsubstantially surrounds a portion of side surfaces of said magneticdisks so as to permit movement of said arms and which is concentric withsaid magnetic disks so as to define a gap between said shroud and saidportion of the side surfaces of said magnetic disks, said arcuate-shapedshroud having portions delimiting an open space therebetween which isadjacent another portion of the side surfaces of said magnetic diskslocated on a downstream side of said arms relative to an air flow whichis generated by the revolution of said magnetic disks and moves onsurfaces of said magnetic disks, a signal wire terminal being disposedin said open space and spaced from a portion of an inner wall and fromsaid arms, an opening provided on said shroud on an upstream side ofsaid arms relative to said airflow and having a greater width than thatof said gap defined between said magnetic disks and said shroud, and acover which constitutes a part of said shroud covers a voice coil motorfor driving said rotary actuator and is spaced from another portion ofsaid inner wall of said housing so as to form a bypass channel betweensaid cover and the another portion of said inner wall of said housingfor providing communication and air flow between said opening and saidopen space including at opposite sides of said signal wire terminal soas to provide air flow to said disks in the region of said open space ata reduced pressure on a downstream side of said arms with respect to thepressure at the upstream side of said arms, wherein said bypass channelhas a linear section of a predetermined length extending from saidopening so as to provide a rectifying effect on air flow therethrough,and wherein said gap defined between the outer peripheral end surfacesof the magnetic disks and said shroud is in a range of 0.1 mm to 0.6 mm.2. A magnetic disk apparatus of claim 1, wherein said bypass channel hasa depth of 5D or more in a direction parallel to a rotating shaft whereD is a width of said linear section.
 3. A magnetic disk apparatus ofclaim 1, wherein said bypass channel has a linear section having alength of at least 5D or more where D is a width of said linear section.4. A magnetic disk apparatus of claim 1, wherein said bypass channel hasa linear section having a depth of 5D or more and a length of at least5D or more in a direction parallel to a rotating shaft where D is awidth of said linear section.
 5. A magnetic disk apparatus of claim 1,wherein said cover covers at least a side surface of said voice coilmotor.
 6. A magnetic disk apparatus of claim 1, wherein said cover is acomponent which at least partially encloses a coil section of said voicecoil motor and at least a side surface of which is closed to preventairflow from coming into said voice coil motor from said bypass channel.7. A magnetic disk apparatus of claim 1, wherein said open space at saidanother portion of the side surfaces of said magnetic disks correspondsat least to a length of the downstream side of said arms.
 8. A magneticdisk apparatus of claim 7, wherein said open space includes a region ofa rotary shaft of said rotary actuator.
 9. A magnetic disk apparatus ofclaim 1, wherein said gap is larger than 0.1 mm and smaller than 0.6 mm.